1. Field of the Invention
The present invention relates to a ratchet tensioner used to provide an appropriate tension to a timing belt or a timing chain of a vehicle engine, and more particularly to a ratchet tensioner having a mechanism for locking and releasing a plunger.
2. Description of the Related Art
The ratchet tensioner has been widely used for suppressing vibrations generated when a timing belt or a timing chain is traveling to transmit rotation between a crankshaft and a camshaft of an engine, and for maintaining an appropriate tension in the timing belt or chain. Such ratchet tensioner is constructed such that a plunger protruding from a housing of the tensioner presses the rear side of a free end portion of a tensioner lever pivotally mounted to a body of the engine, so that a shoe surface of the tensioner lever slidably contacts with a slack side of the chain to give an appropriate tension to the chain (see Japanese Patent Publication No. HEI-3-8415, Japanese Patent Laid-Open Publication No. HEI-10-2386, and Japanese Patent Laid-Open Publication No. HEI-11-344086).
A typical example of the known ratchet tensioners is shown in FIGS. 5 and 6. The tensioner 31 includes a housing 32, a plunger 33 slidably mounted in the housing 32 and urged by a plunger spring 36 so that one end 33A of the plunger 33 projects outward from the front surface of the housing 32. The tensioner 31 further has a ratchet pawl body 34 pivotally mounted by a shaft 34A to the housing 32 and urged by a ratchet pawl spring 38. The ratchet pawl body 34 has a ratchet pawl 34B engaged with a ratchet tooth 33B formed on a side surface of outer periphery of the plunger, so that a backward displacement of the plunger 33 is suppressed.
The ratchet tensioner 31 includes a buffer mechanism using a flow resistance of oil, and a backlash is maintained between the ratchet tooth 33B and the ratchet pawl 34B, so that the oil (not shown) is introduced into the interior of the plunger 33 from an external oil pump operating in synchronism with the engine via a check valve mechanism 35. When the plunger 33 receives shock from the tensioner lever, the plunger 33 is retracted against the force of a plunger spring 36 within a range of the backlash in a state that the ratchet tooth 33B and the ratchet pawl 34B are engaged. At that time, the check valve mechanism 35 is closed to leak the oil in the plunger 33 from between the outer peripheral surface of the plunger 33 and the inner peripheral surface of a plunger-accommodating hole of the housing 32, so that a shock force is relieved. Furthermore, reference numeral 32B in FIGS. 5 and 6 indicates a mounting hole for mounting the ratchet tensioner 31 to the engine body.
Additionally, the ratchet tensioner 31 comprises a plate 37 secured to an end of the shaft 34A of the ratchet pawl body projecting outside the housing 32. When the ratchet tensioner 31 is shipped or to be mounted to the engine, as shown in FIGS. 7 and 8, a stopper pin 39 is inserted into a pin inserting hole 37A of the plate 37 to contact with an outer wall end surface 32A of the housing 32 in a state that the ratchet tooth 33B and the ratchet pawl 34B are engaged, and thus the plunger 33 is retained so as not to fly out from the housing 32. In this case, after mounting the ratchet tensioner 31 to the engine, the stopper pin 39 is removed to place the tensioner 31 in an operating condition.
Furthermore, as other means for holding the plunger 33 in position against movement in the projecting direction when shipping the ratchet tensioner, as shown in FIGS. 9 and 10, the ratchet pawl body 34 is rotated by the rotation of the outer plate 37 to engage the ratchet tooth 33B with the ratchet pawl 34B, and then the stopper pin 39 is inserted through the pin inserting hole 37A of the outer plate 37 into a stopper hole 32C formed in the housing 32.
In the ratchet tensioner, it is necessary to pull in the plunger 33 that has been projected in case of repairing the engine, removing or mounting the chain. However, the prior ratchet tensioner has problems that the plunger 33 cannot be pushed simply into the interior of the housing, and the work for removing or mounting the chain cannot be performed simply, since the outer plate 37 is rotated to rotate the ratchet pawl body 34 so that it is possible to release the engagement of the plunger 33 serving as one-way mechanism, but there is not a mechanism for maintaining the state in that the engagement is released. Furthermore, it is difficult to insert a driver from a small window hole such as an engine service hole etc., for rotating the outer plate, and it is not capable of maintaining the disengagement state of the plunger.
Therefore, in view of the aforementioned problems, an object of the present invention is to provide a ratchet tensioner including a plunger locking and releasing mechanism which is capable of holding a plunger selectively in a locking position where a ratchet pawl on the ratchet pawl body is in interlocking engagement with ratchet teeth on the plunger, and in a releasing position in which the ratchet pawl is disengaged from the ratchet teeth.
To accomplish the above object, according to the present invention, there is provided a ratchet tensioner comprising: a housing; a plunger retractably mounted in the housing with one end projecting outward from the housing, the plunger having a series of ratchet teeth formed on an outer peripheral surface thereof; a plunger spring acting between the housing and the plunger and urging the plunger in a direction to project outward from the housing; a ratchet pawl body pivotally mounted by a shaft to the housing, the ratchet pawl body having a ratchet pawl formed at one end of the ratchet pawl body; a ratchet pawl spring acting between the housing and the ratchet pawl body and urging the ratchet pawl body to turn about the axis of the shaft in a direction to engage the rachet pawl with the ratchet teeth on the plunger, thereby preventing the plunger from moving backward; and a plunger locking and releasing mechanism for selectively locking and releasing the plunger with respect to the ratchet pawl.
The plunger locking and releasing mechanism has a pin-accommodating hole formed in an outside surface of the housing, an actuator plate disposed above the outside surface of the housing and secured to the shaft of the ratchet pawl body for co-rotation with the shaft and the ratchet pawl body, the actuator plate having a pin-insertion hole of a diameter smaller than the pin-accommodating hole, the actuator plate being manually movable about the axis of the shaft in opposite directions between a locking position in which the pin-insertion hole is in substantial alignment with the pin-accommodating hole and the engagement between the ratchet pawl and the ratchet teeth is maintained, and a releasing position in which the pin-insertion hole is out of alignment with the pin-accommodating hole, and the ratchet pawl is released from interlocking engagement with the ratchet teeth against the force of the ratchet pawl spring, a stopper pin removably inserted into the pin-accommodating hole either through the pin-insertion hole to keep the actuator plate in the locking position, or alternatively directly, with an outer edge of the actuator plate being in contact with the stopper pin, to keep the actuator plate in the releasing position.
In the ratchet tensioner of the foregoing constitution, the actuator plate is rotated to maintain interlocking engagement between the ratchet pawl and the ratchet tooth, so that the stopper pin is inserted into a pin-inserting hole of the actuator plate and a pin-accommodating hole of the housing, thereby maintaining the plunger in its engaged state. The plunger is prevented from moving forward in the projecting direction. When the actuator plate is rotated to disengage the ratchet pawl from the ratchet tooth, the stopper pin contacts with an outside end surface of the actuator plate and fitted into the pin-accommodating hole of the housing, thereby allowing the plunger to project from the housing or simultaneously maintaining the plunger to be pushed into the housing.